Roofing shingles are traditionally manufactured utilizing asphalt, which is derived from crude oil. Asphalt prices have recently increased even more rapidly than crude oil prices. In addition to the use and cost of crude oil in the asphalt manufacturing process, the process of manufacturing asphalt shingles further utilizes a considerable amount of fossil fuels heating both the asphalt and the fillers so that they can be combined. Typically, approximately 65% filler is mixed with approximately 35% asphalt. In order to create a mixture having a usable viscosity, the asphalt is heated to 450° F. while the filler is heated to approximately 350° F. prior to the two additives being mixed together.
Considerable waste is involved with the manufacture and use of asphalt roofing materials, such as shingles and roll roofing membranes. For example, each new asphalt roofing shingle has cutout tabs that are removed and discarded (this waste will be called “manufacturer's asphalt roofing shingle waste”) while old shingle materials removed from existing buildings (this waste will be called “post consumer asphalt shingle waste”) also adds to a significant amount of roofing material waste. In the US alone, 11 million tons of post consumer asphalt shingles are removed from roofs annually. Approximately 10 million of these tons are buried in landfills. Not only are landfill costs increasing, but access to landfills for recyclable products is becoming more restricted since roofing shingles are products which do not degrade. Asphalt shingles pose an additional particular problem to landfills because they restrict natural water movement causing delays with the natural decay of other items in the landfill. The asphalt shingles themselves do not degrade and stay permanently in the landfill.
Recycling of all types of roofing material waste has been discussed and attempted but has not been terribly successful. The waste generated from asphalt roofing materials presents a significant recycling as well as environmental concern because of the composition of the roofing material. Typical shingles are composed of a cellulose fiber saturated with asphalt or fiberglass mat, an asphalt coating on the mat, and granules disposed on the coating. Such materials are difficult to break down and have typically required complex recycling processes.
Past attempts at recycling asphalt shingles have failed to reduce the shingle granules to a size small enough for the recycled shingle material to be reused. If the granules in the recycled shingle material are not reduced to a fine powder, the granules will not remain suspended in an asphalt solution and the recycled shingle material cannot be reused in roofing or other products. Too fine of a granule also poses a problem in that the fine material does not have a significant use and is therefore not sellable.
Some past methods of recycling asphalt roofing material have used milling machines, such as rolling mills, bag mills, hammer mills, saw mills, etc. to produce a recycled roofing material which can be used only in road construction or as other similar “filler” material. However, merely milling the shingle material in a reduction mill without further processing has been unsuccessful in reducing the granules in the shingle material to a fine mesh so that the recycled asphalt can be reused in manufacturing new roofing products.
Asphalt roads are comprised of six percent paving grade asphalt and ninety-four percent aggregate. The particle size distribution is very specific and is carefully monitored by state and federal agencies. Attempts to use post factory and post consumer shingles have been stopped by four major issues. First, ⅜ inch chips (the standard currently in use) will not dissolve in the mixing process, so little asphalt is freed up for incorporation into the road (the entrained mix energy is lost) which causes the amount of asphalt and mineral to be inconsistent. Second, the plastic Mylar on the back of all shingles is left as 4-5 inch by 1 inch pieces. Third, the nails may not be removed and fourth, the shingles contain too many fines. All of these issues create their own series of problems in recycling the materials for reuse. Nails cannot be present in the recycled material that is to be used, as nails in a road would pose serious problem. Likewise, the presence of fines in pavement creates air pockets and voids that affect the HMA performance in terms of rutting and cracking. Shingles contain 30-40 percent fines and the amount of fines needs to be reduced as low as possible because the fines increase viscosity causing more roller energy to be required (more passes over the pavement while hot) and they can have serious road quality implications. A new process is needed that resolves all of these issues.
One such apparatus for recycling roofing shingles is disclosed in U.S. Pat. No. 4,706,893 to Brock. This apparatus includes a hammer mill that comminutes the shingles and a vessel that subsequently dries then mixes the recycled shingle material with liquid asphalt, for recycling as an asphalt paving composition. This milling process will not reduce the granules in the shingle material to a small enough size for the shingle material to be reused in applications other than an asphalt paving composition. Moreover, portions of the recycled material that is too fine is considered “fines” in the paving industry and are unwanted in that they significantly increase the viscosity of the paving mixture and must be washed off or takes significantly more time to pack down.
Another shingle reducing apparatus is disclosed in U.S. Pat. No. 5,385,426 to Omann. This complex apparatus includes a shredder, two hammer mills, and two heated vessels for drying the shingle material after it has been reduced. This apparatus further requires spraying the shingles with water prior to entering the first hammer mill. This extremely complex and involved process requiring two hammer mills also is not capable of completely reducing the granules in the recycled shingle material to a fine mesh or powder.
One reason milling machines have been unsuccessful in reducing the granules in the recycled shingle material is because the shingle material was not heated as it was milled. In the past, heating the milling machine as the shingle material is milled was considered hazardous because of pressure build up in the closed milling vessel or heating vessel as a result of moisture in the shingle material. Heating would also make hammer mills gum up and not work because the asphalt would become sticky.